The Ising chain in a transverse field is a paradigmatic model for a host of physical phenomena, including spontaneous symmetry breaking, quantum criticality and duality. Although the quasi-one-dimensional ferromagnet CoNb₂O₆ has been regarded as the Ising chain’s best material realization, it exhibits substantial deviations from ideality. By combining terahertz spectroscopy and calculations, we show that CoNb₂O₆ is in fact described by a different model with bond-dependent interactions, which we call the ‘twisted Kitaev chain’, as these interactions are similar to those of the honeycomb Kitaev spin liquid. The ferromagnetic ground state of CoNb₂O₆ arises from the compromise between two axes. Owing to this frustration, even at zero field domain walls have quantum motion, which is described by the celebrated Su–Schriefer–Heeger model of polyacetylene and shows rich behaviour as a function of field. Nevertheless, close to the critical field, this model enters a universal regime in the Ising universality class. We observe that the excitation gap in the ferromagnet closes at a rate twice that of the paramagnet. This universal ratio originates in the Kramers–Wannier duality between domain walls and spin flips, and in the topological conservation of domain wall parity. Our work also shows that Co²⁺ magnets are fertile ground in the search for quantum spin liquids.

横向场中的伊辛链是一系列物理现象的范式模型，包括自发对称性破缺、量子临界性和对偶性。尽管准一维铁磁体CoNb ₂ O ₆被认为是伊辛链的最佳材料实现，但它与理想状态存在很大偏差。通过结合太赫兹光谱和计算，我们表明 CoNb ₂ O ₆实际上是由具有键依赖性相互作用的不同模型描述的，我们称之为“扭曲的 Kitaev 链”，因为这些相互作用类似于蜂窝状的 Kitaev 自旋液体。CoNb ₂ O _{6的铁磁基态}源于两个轴之间的妥协。由于这种挫折，即使在零场域壁也有量子运动，这由著名的聚乙炔 Su-Schriefer-Heeger 模型描述，并显示出丰富的场函数行为。然而，在接近临界场的情况下，该模型进入了 Ising 普遍性类中的普遍制度。我们观察到铁磁体中的激发间隙的闭合速度是顺磁体的两倍。这种普遍的比率源于畴壁和自旋翻转之间的 Kramers-Wannier 对偶性，以及畴壁奇偶性的拓扑守恒。我们的工作还表明，Co ²⁺磁体是寻找量子自旋液体的沃土。